84 MAGNETIC SURVEY OP TASMANIA. 



that a state of affairs obtained in Tasmania similar to 

 that in Victoria. If the same weight be attached to Sir 

 J. Lefroy's determination as to that of Dr. Neumajer, we 

 should have that, during the period under discussion, 

 the annual average rate of change of declination 

 was no less than 5' — assuming that the maximum declina- 

 tion was neached in 1863 — the most suitable hypothesis 

 for reducing the change of declination to a minimum. 

 Seeing that the annual rate of change in Victoria 

 between 1866 and 1881 only amounted to 2', it is diffi- 

 cult to accept for Tasmania an annual average rate of 

 change so large as 5'. The explanation may lie in the 

 rough method of determination employed by Sir J. 

 Lefroy ; at all events, it is a matter of some importance 

 that this difficulty should be cleared up. 



If any magnetic measurements were made by the 

 American expedition to Hobart to observe the transit of 

 Venus in 1874, I have been unable to find them. The 

 same remark applies to the observations made by the 

 Austrian scientific expedition which visited Hobart 

 between two and three years ago. As, however, the obser- 

 vations of the lastmentioned party were made at the Obser- 

 vatory, where the highly magnetic greenstone outcrops, 

 their results are quite valueless for the purposes of com- 

 parison with those of Kay and Neumayer. 



The results of the observations taken by Lieutenant 

 Colbeck and Mr. Bernacchi of the Soiithern Cross, during 

 the recent stay of that vessel in Hobart, have not yet 

 reached me. 



This brief summary of the history of magnetic research 

 in Tasmania shows that during the visit of the Royal 

 Society of London's expedition both the dip and the 

 horizontal intensity passed through minimum values, and 

 leads us to infer that after Dr. Neumayer's visit the 

 declination passed through a maximum value, but when 

 this occurred we do not know, and what is the present 

 annual rate of change of the declination we do not know 



II. — Maqnetic loork in Victoria and Neiv Zealand. 



Absolute magnetic measurements were first begun in 

 Victoria, in 1858, by Dr. Neumayer. Between that date 

 and February, 1863, he carried out, without interruption, 

 hourly readings of the magnetic elements, these difi^eren- 



